1. Field of the Invention
This invention relates to the field of data processing systems. In particular, this invention relates to the placement of circuit board modules in data processing systems.
2. Art Background
In recent years manufacturers of data processing systems have strived to design and package systems to be compact and easy to service and upgrade at the end user site. Compact designs are desirable because they are easily utilized in an office environment where the availability of space and special environmental conditions required by mainframe computers is limited. In addition, data processing systems are typically marketed with a number of options available. The end user may wish to add or remove options at any time after initial installation. It is desirable that the field service representative or end user be able to easily make changes in the field in the minimum time possible without the need for special tools.
A common method of achieving the goals of compact design and ease of field service and field upgrades is to employ a modular circuit board design. A common type of modular design provides for a main circuit board which may be referred to as the "motherboard". The motherboard usually contains the basic computer circuitry essential for operation of the data processing system. One or more additional circuit boards are used to provide optional or enhanced functions. The circuit boards containing circuitry necessary to accomplish the optional functions can be referred to as "daughterboards". Daughterboards can be electrically connected to the motherboard over multipin bus connectors.
As an example, a daughterboard may serve as an interface to an optional printing device for the data processing system. In a modular system, the optional printing device can be added at the end user site by adding the printer interface module as a daughterboard to the data processing system. The printer interface daughterboard can be coupled to the motherboard over a multi-pin bus connector to provide data and control for the printer. The printer daughterboard may have a printer connector attached or may have a cable that can be routed to an accessory panel that provides the printer connector.
Some modular designs position daughterboards side by side above and parallel to the motherboard. This configuration in some circumstances can limit the speed of data transfer between motherboard and daughterboard. For example, memory expansion of a data processing system may require the use of more than one daughterboard. Side by side placement of daughterboards can complicate routing of motherboard bus signal traces that carry bus signals to the daughterboard connectors. Tids results in increased length of signal traces on the motherboard and a consequential limitation of data transfer speed. Moreover, closely spaced side-by-side daughterboards are difficult to properly remove by hand because of the difficulty of getting a grip on the daughterboard. In addition, daughterboards can work loose from the motherboard bus connectors during shipment, creating the need for means to retain the daughterboards onto the bus connectors. Past means for retaining the daughterboards have involved the use of screws or spring clips. However, these types of retaining means complicate the installation and removal of daughterboards in the field because of their need for special tools. Further, removal of spring clips of fasteners necessarily requires use of one or both hands of the person installing or removing daughterboards, thereby requiring another person, or alternatively a special tool, to manipulate the daughterboard.
As will be more fully described in the following detailed description, the present invention permits flexible placement of modular circuit boards in order to provide for minimal bus signal path lengths, and to provide for ease of installation and removal of circuit boards.